Inductive device



March 18, 1958 HENDERSON 2,827,615

INDUCTIVE DEVICE Filed Nov. 7, 1955 2 Sheets-Sheet 1 izvmvrox. I Mme Z Roy fi/avpczson/ ATTORNEY March 18, 1958 HENDERSON 2,827,615

INDUCTIVE DEVICE Filed Nov. 7, 1955 2 Sheets-Sheet 2 INVENTOR. MA YNE [55 Pay l/evweRso/J ATTORNEY United? States Patent INDUCTIVE DEVICE Wayne Lee Roy Henderson,

Danville, Ill., assignor to General Eiectrie Company,

This invention relates to inductive devices such as transformers and reactors and to the magnetic core members for such devices. More particularly, my invention relates to high-reactance, shell-type transformers used as ballasts for arc-discharge devices such as fluorescent lamps wherein shunts of magnetic material provide the high-leakage reactance of the device.

In a copending application Serial Number 510,765 filed May 24, 1955, by Roy H. Dlerstein, there are described a number of inductive devices each having a laminated core configuration which enables the laminations thereof to be successively cut off from a strip of magnetic material substantially without scrap. In one embodiment of the invention covered by this Dierstein application, a magnetic core construction is described having a center stack of i laminations and a pair of yoke stacks of laminations defining a pair of coil receiving windows with the central stack. Each yoke lamination has a pair of axially aligned straight portions connected by angular connecting portions to a central laterally offset straight portion which bears against or is in close proximity to the center of the I lamination thereby to form a magnetic shunting path therewith. The angular relation between these straight portions and the connecting portions permit the laminations to be successively cut oil from the strip of magnetic material without scrap. However, where a coil having flat rather than tapered oppositeend surfaces is employed, in this Dierstein construction there is a waste of space in the region of the angularly disposed connecting portions.

Accordingly, one object of the invention is to provide a magnetic-core construction of a high-reactance transformer having an integral magnetic shunt and composed of stacks of scrapless laminations of reduced length and with reduced waste space in the coil-receiving windows thereby to provide a smaller, lighter and less expensive device.

Another object of the invention is to provide a magnetic-core construction for an inductive device formed of a plurality of stacks of central and yoke laminations which define a hole substantially centrally of the device, which hole may be utilized for various purposes such as for supporting a connecting or terminal member or for permitting central mounting of the device.

Another object of the invention is to provide a transformer having a pair of coils arranged side by side on a common core and having simple and convenient means for making connection to and between the leads of said coils.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by referring to the following description taken in connection with the ac: companying drawings in which- Figure 1 is a plan view of a ballast transformer embodying the invention,

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Figure 2 is a sectional view of the core and coil assembly of the transformer of Figure 1,

Figure 3 is an end view of the transformer of Figure 1 with the core-retaining end clip removed,

Figure 4 is a diagrammatic plan view of a strip of magnetic material illustrating by dashed lines how the yoke laminations may be successively cut oif from strip material without scrap.

Figure 5 is a view similar to Figure 4 illustrating how the central stack laminations may likewise be punched from strip material of the same width without scrap.

Figure 6 is a plan view of a central portion of a transformer construction illustrating the use of the central hole of the core thereof for supporting a coil connecting and terminal member.

Figure 7 is a detailed perspective view of the connector member employed in the transformer of Figure 6, and

Figure 8 is a side cross-sectional view of a central portion of an enclosed transformer construction utilizing the core and coil assembly of Figure 1 and illustrating how the central hole may be employed for mounting the transformer.

Referring to Figure 1, one form of the invention is shown embodied in a high-reactance ballast transformer 10 of the type suitable for use in electrical ballast circuits such as disclosed in Patent 2,578,395, granted December 11, 1951, to W. W. Brooks. Transformer 10 has a magnetic-core construction including a pair of abutting central stacks of laminations 11 and a pair of outer yoke stacks of laminations 12 forming coil receiving windows 13 therewith. Suitable coils 14 constituting the primary and secondary windings of transformer 10 are supported in side-by-side relation on the central stacks of laminations 11 within windows 13. Connector pads 15 having terminals 16 for making connections to and between the leads of coils 14 may be conveniently supported on the outer covering 17 of the coil, as shown. Metal retaining spring clips or caps 18 are pressed over the opposite ends of the central and yoke stack laminations to hold the entire assembly together as well as tightly to compress the laminations.

In accord with the invention, the central core member for supporting the coils 14 comprises a pair of abutting stacks of identical laminations 11 rather than a single stack of I-shaped laminations. Each central stack lamination comprises an elongated strip having two straight portions 19 and 20 joined by an integral central portion 21 angularly offset outwardly from said straight portions, thereby to define a hole 22 within transformer 10 and preferably substantially centrally thereof. Angularly offset portion 21, of each central stack lamination, preferably is V-shaped, as shown, with opposing straight edges 23 and 24 respectively parallel to one another. Referring to Figure 5, it will be noted that with this configuration, the opposite edges of each central stack lamination are complementary and parallel to one another along their entire length such that they may be successively cut off from a strip of magnetic material 25 without scrap.

As shown in Figure 4, laminations 12 of each outer yoke stack are likewise identical and capable of being successively cut oif from a strip of magnetic material 26 without scrap. Each yoke stack lamination 12 has a pair of axially aligned straight end portions 27, 27 and a pair of axially aligned straight body portions 28 laterally offset from said end portions 27, 27' and connected thereto by integral angularly disposed connecting portions 29. One of the end portions 27 of each yoke stack lamination has an inner tip projection 27a which bears against the side of one end portion of central stack lamination 11 and has an adjacent recess 27b which forms a small non-magnetic gap therewith. A small notch 27c in the upper end of portion 27 conforms to the tip projection 27a. The opposing edges of each portion 2.7, and 29, respectively, form straight lines parallel and complementary to one another. The two straight body portions 28 are joined by a central portion 39 angularly olfset inwardly of the transformer to meet or come into close proximity with the outwardly offset angular central portion 21. Central portion 30 of yoke stack lamination 12 preferably has a W -shape, as shown, such that its bottom edge 31 conforms and dovetails with the outer edges 25, 24 of the center stack lamination central portion 21 but preferably in closely spaced relation thereto thereby to provide a non-magnetic gap 31a therebetween. Gap 31a may be an air gap or filled with non-magnetic material, as shown. The opposing edges defining this central portion 3% also form straight lines parallel and complementary to one another such that the entire yoke lamination 12 may be cutoff from strip material 26 without scrap.

it will be appreciated that the amount of waste space 33 in the coil receiving windows 13, when coils 14 having fiat rather than tapered end surfaces 34 are employed depends to a considerable extent upon the amount of angular displacement of the central portion 30 and connecting portions 29 of the yoke stack laminations 12 relative to their straight portions 27, 23. As the angles A, shown in Figure 2, approach right angles the amount of waste window space 33 decreases but the width of the angular connecting and central portions 29 and 30 also decreases if the opposite edges of these portions are kept parallel and complementary to one another. in order to provide suiilcient cross section at these connecting and central portions, not unduly to restrict the magnetic flux in the core, it is necessary that the angles formed between these connecting and straight portions remain obtuse, for example, in the neighborhood of 135 degrees. However, because of the nested arrangement of the outwardly extending t -shaped central portion of the center lamination 1i and the W-shaped central portion 39 the yoke lamination 12, the amount of wasted coil window space 33' near the center of the transformer is considerably reduced.

This nested construction also permits a general shortening of the device without reduction in the leakage reactance thereof provided by the magnetic shunting path between the center and yoke laminations. More particularly, the minimum cross-sectional dimension of this magnetie shunting path is represented by the distance d in the construction of Figure 2. If a rectangular 1 center lamination were used instead of one having the outwardly offset central portion 21 it would be necessary for both the center and yoke laminations to be slightly longer, in order to achieve the same minimum cross-sectional dimension d of the magnetic shunting path. The construction of the invention thus enables narrower strip materials 25, 26 to be used from which the yoke and center laminations are extracted over that which would be required by prior scrapless constructions. When these transformers are made under modern mass production techniques, such small savings in unit cost become very important.

Referring now to Figures 6 and 7 there is shown a further embodiment of the invention in which the central hole 22 defined by the center stack laminations 11 is used to support a terminal member for the coils of the transformer. The transformer 32 of Figure 6 is identical with that shown in Figure l with the exception that coils 35 having fewer windings are shown and the connecting pads 15 are omitted. Transformer 32 may, for example, be used in a ballast circuit such as disclosed in United States Patent 2,334,587, granted November 16, 1943, to T. T. Short. In this embodiment of the invention a generally T-shaped terminal member 36 is employed to make the connections to and between the leads of coils 35.

Terminal member 36 comprises an insulating foldable rectangular sheet, such as cardboard or fiber, having conductive metal tabs 37 riveted at spaced points along the top edge portion. The opposite sides of the insulating sheet are cut and folded in opposite directions from the main body or stem 38 to form supporting flanges 39 and 46 respectively. The width W of the main stem 38 is equal to the diagonal dimension of hole 22 such that when stem 38 is inserted within square hole 22 the flanges 39 and 49 bear against opposing inner walls of the central stack laminations 11 defining hole 22. The leads 41 of the coils 35 are then soldered or otherwise connected to the conductive metal tabs 37 as desired.

Referring now to Figure 8, I have shown a further embodiment of the invention wherein a transformer 10 of Figure 1 is encased within a suitable housing and the central hole 22 is employed to permit mounting the resulting enclosed transformer. In Figure 8, only the central portion of transformer 10 is illustrated. A rectangular metal housing 42 is provided having a base member 43 and a cover member 44, both members having their central portions drawn inwardly to form central hollow cylinder portions 45 and 46 respectively which register and communicate with square hole 22. Any suitable fastening means such as bolt 47 and nut 48 may then be employed to fasten and mount the enclosed transformer 10 to a suitable support 49.

Although I have described above specific embodiments of the invention many modifications may be made. I intend, therefore, by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A magnetic-core structure for an inductive device comprising a pair of abutting central stacks of elongated laminations each having two straight axially aligned portions for supporting coils thereon joined by a center portion offset outwardly from said straight portions whereby said offset portions of said abutting central stacks define a hole thcrethrough, and a pair of yoke stacks of elongated laminations supported on opposite sides of said abutting central stacks in magnetic circuit relation therewith, said yoke stacks having portions spaced from and defining coil receiving windows with said central stacks and having a central portion extending in close magnetic relation with sa dI offset portions to form magnetic shunting paths therewit 2. A magnetic-core structure for an inductive device comprising a pair of abutting central stacks of elongated strip laminations forsupporting coils of said device, each central stack lamination having two straight axially aligned portions joined by an integral portion angularly offset outwardly from said straight portions wherebysaid abutting central stacks of laminations define a hole within said device, and a pair of yoke stacks of elongated laminations extending on opposite sides of said central stack with opposite ends of each yoke stack supported against and in magnetic circuit relation with one of said pair of abutting central stacks, each yoke stack lamination constituting a strip of substantially constant width having two straight axially aligned portions spaced frorn said central stacks and joined by an integral portion angularly offset inwardly from said straight portions and in close-magnetic relation with the angularly offset portions of said central stack laminations to form magnetic shunting paths therewith.

3. The magnetic-core structure of claim 2 wherein the angularly offset portion of each central stack lamination is V-shaped and the angularly offset portion of each yoke stack lamination is JV-shaped.

4. The magnetic-core structure of claim 3 wherein the opposing edges defining the offset V-shaped portion of each central stack laminations are straight and parallel to one another whereby the laminations may successively cut oti from a strip of magnetic sheet material without scrap.

5. The magnetic-core structure of claim 3 wherein the opposing edges defining the offset W-shaped portion of each yoke stack lamination are straight and parallel to one another whereby these laminations may be successively cut off from a strip of magnetic sheet material without scrap.

6. The magnetic-core structure of claim 3 wherein the V-shaped portions of the central stack laminations and the W-shaped portions of the yoke stack laminations have edges conforming and extending in closely spaced relation with one another to form non-magnetic gaps therebetween.

7. A shell-type inductive device comprising a pair of abutting central stacks of elongated laminations each having two straight axially aligned portions joined by an integral portion offset outwardly from said straight porti-ons whereby said abutting central stacks define a hole within said device, coils supported on said straight portions of said central stacks, a pair of yoke stacks of elongated laminations in magnetic circuit with said central stacks extending on opposite sides of said coils, and a terminal member having a supporting portion extending within said hole in contact with the sides of said central stacks defining said hole, said terminal member having means for making connections to and between said coils.

8. The device of claim 7 wherein said terminal member comprises insulating material and has a generally T- shape, and the connecting means constitutes spaced-conductive tabs fastened along the top of said member.

9. An inductive device comprising a magnetic core having a pair of abutting central stacks of elongated laminations and a pair of yoke stacks of elongated laminations supported on opposite sides of said abutting central stacks in magnetic circuit relation therewith, said yoke stacks having portions spaced from said central stacks and defining coil receiving windows therewith, each central stack lamination having two straight axially aligned portions joined by a center portion offset outwardly from said straight portions and in close magnetic relation to said yoke stack laminations to provide magnetic shunting paths therewith and to define a hole within said core, said device having mounting means extending through said hole.

References Cited in the file of this patent UNITED STATES PATENTS 

